Method for producing vattable organic pigments

ABSTRACT

The invention relates to a method for producing vattable organic pigments. The invention is characterised in that an aqueous or an aqueous-organic suspension of a coarse crystalline raw mineral is vatted and re-oxidised, and the pigment suspension is ground to a diameter equal to or less than 0.9 mm during vatting and/or during oxidation by means of an agitator ball mill, which is operated at a power density of more than 1.0 KW per litre per grinding chamber and at an agitator peripheral speed of more than 12 m/s, using grinding bodies.

The present invention relates to a new method of fine division oforganic pigments.

Many organic pigments are obtained from their synthesis in the form ofcoarsely crystalline crude pigments. In order to bring them into a formin which they can be used practically, it is necessary to reduce theparticles in size. A variety of methods are known for this purpose inthe literature.

DE-2 727 484 discloses a method of fine division ofperylene-3,4,9,10-tetracarboxylic acid N,N′-bismethyl imide byrevatting.

DE-2 803 362 discloses a method for fine division especially for the twopigments perylene-3,4,9,10-tetracarboxylic bis-p-phenetidide andbis-p-chloroanilide by oxidizing the leuco form in the presence ofsurfactants or exposure to shearing forces. Shearing forces are producedby dispersing mills customary at that time.

DE-2 854190 discloses a method through oxidation of the leuco compoundof indanthrone pigments with simultaneous exposure to shearing forces.The presence of surfactants is required. The shearing forces areproduced by dispersing mills customary at that time.

In EP-1 76 899 the fine division method employed is a customary saltvibration milling. The large amounts of salts used burden thewastewater.

EP-213 281 describes a method of fine division of pigments of theanthanthrone series by revatting with a subsequent solvent finish. Thisis a two-stage method for one individual pigment class. The use of asolvent necessitates technically demanding apparatus for solventrecovery.

EP-678 559 discloses a fine division method for organic pigments wherethe pigments are first subjected to dry milling and the resultingprepigments are wet-milled in aqueous suspension in a stirred ball millwith a high power density. The two-stage method requires long operatingtimes. Dry milling is associated with considerable production of dust,which is problematic from the standpoint of occupational hygiene.

EP-702 060 discloses a method of producing 4,10-dibromoanthanthronepigments using a stirred ball mill with high power density.

EP-979 846 discloses a method of producingN,N′-dimethylperylene-3,4,9,10-tetracarboxylic diimide using a stirredball mill with high power density and employing one or more additivesfrom the group of the pigment dispersants and surfactants.

DE-100 05 186 discloses a method of producingperylene-3,4,9,10-tetracarboxylic diimide using a stirred ball mill withhigh power density.

The use of pigments for coloring high molecular mass organic materialsimposes exacting requirements on the performance properties of thepigments, such as high color strength, excellent overcoating fastnessesin the case of using coating systems, high gloss, low viscosity of thehighly pigmented paint concentrates (milbase) and, particularly in thecase of metallic finishes, high transparency and brilliant colors. Theyshould also be able to be used as far as possible universally in thedifferent varnish systems. In the case of coloring of plastics there isa demand, in addition to the coloristics and the fastness propertiessuch as bleedfastness, for ready dispersibility in particular.

The methods disclosed in the publications referred to above are in somecases intended only for specific pigments and in some cases associatedwith drawbacks such as multiple stages, long operating times, use ofsolvent or large quantities of salt, which is reflected in increasedcosts.

There was a need for improvement and hence the object of finding amethod of fine division of vattable organic pigments which is animprovement on the prior art, being more cost-effective, whose use isnot restricted to a specific pigment, and which provides pigments whichsatisfy the requirements in terms of performance properties.

It has been found that the object is achieved surprisingly throughcombination of vatting with wet milling with a stirred ball mill of highenergy density.

The invention provides a method of producing vattable organic pigmentswhich comprises vatting an aqueous or aqueous-organic suspension of acoarsely crystalline crude pigment and reoxidizing it, the pigmentsuspension being milled during vatting and/or oxidation by means of astirred ball mill which is operated with a power density of more than1.0 kW, in particular more than 1.5 kW, per liter of milling space andwith a peripheral stirrer speed of more than 12 m/s, under the action ofgrinding media with a diameter of less than or equal to 0.9 mm.

By vatting is normally meant a reduction of the colorant, the color ofthe reduced colorant generally being different from that of theunreduced original colorant.

The method of the invention relates to all organic pigments which can bevatted, examples being indanthrones, such as C.I. Pigment Blue 60;anthanthrones, such as C.I. Pigment Red 168; thioindigo, such as C.I.Pigment Red 88,181, C.I. Vat Red 41 and C.I. Pigment Blue 66; perinones,such as C.I. Pigment Orange 43, C.I. Pigment Red 194 and C.I. Vat Red14; or perylenes, such as C.I. Pigment Red 123, 149, 178, 179 and 189,C.I. Pigment Violet 29 and C.I. Pigment Black 31 and 32, and alsomixtures or mixed crystals thereof.

The coarsely crystalline crude pigments are vatted in aqueous-alkalinesuspension with a reducing agent, such as alkali metal hydrogensulfite,alkali metal dithionite, alkali metal hydroxymethanesulfinate orborohydrides. Preference is given to sodium or potassium dithionite.

The optimum pigment concentration in the suspension is dependent on theparticle size and particle morphology of the pigment and also on therheology of the suspension. It can be from 2.5% to 40% by weight,preferably from 5% to 25% by weight, in particular from 7.5% to 20% byweight, based on the overall weight of the suspension.

The amount of reducing agent can be up to five times the amount requiredstoichiometrically for vatting, though it is preferred to use only from0.1 to 2 times the required amount.

The aqueous-alkali medium is prepared using preferably aqueous solutionsof alkali metal hydroxides, preferably sodium and potassium hydroxidesolution.

The alkali should be used stoichiometrically to the amount of reducingagent, although it is also possible to use an excess of up to 5 times inrespect of the reducing agent.

Reoxidation is carried out using an oxidizing agent in an amount whichis at least stoichiometric relative to reducing agent; it may be up to 5times the stoichiometric amount. Oxidizing agents used are, for example,hydrogen peroxide and adducts thereof, such as sodium perborate; air;oxidizing salts, such as nitrates, chlorates or hypochlorites,especially alkaline hypochlorite solution; oxidizing acids, such asnitric acid; or nitro compounds, such as 3-nitrobenzenesulfonic acid.

Milling takes place at any desired point in time, with the proviso thatit relates to a time period between the beginning of reduction and theend of oxidation. Thus, for example, the reducing agent can be addedwhile milling is ongoing, or milling may follow the reduction. Millingcan also take place during the addition of the oxidizing agent and ifappropriate may continue following complete oxidation until the desiredfineness is reached, or milling operates both during reduction andduring oxidation. The leuco compound can be milled in the form of itssalt and in the form of its acid, which can be deposited after reductionby addition of organic or inorganic acids. Acids suitable for depositingthe leuco form include organic acids, such as aliphatic or aromaticcarboxylic or sulfonic acids, such as formic acid, acetic acid,trichloroacetic acid, propionic acid, butyric acid, hexanoic acid,oxalic acid, citric acid, benzoic acid, phenylacetic acid,benzenesulfonic acid or p-toluenesulfonic acid, and inorganic acids,such as hydrochloric acid, sulfuric acid or phosphoric acid, forexample.

Examples of mills suitable for the milling carried out in the method ofthe invention are stirred ball mills which are designed for batchwiseand continuous operation, which have a cylindrical or hollow-cylindricalmilling chamber in horizontal or vertical construction, and which can beoperated with a specific power density of more than 1.0 kW, inparticular more than 1.5 kW, per liter of milling space, and whoseperipheral stirrer speed is more than 12 m/s. Mills suitable for thispurpose are described for example in DE-C-3 716 587. If the millingintensity of the mill is lower, then the good properties according tothe invention, in particular the outstanding coloristics, such as hightransparency and color strength, and the ready dispersibility of thepigments are not achieved. The energy output per unit time by thestirrer is transmitted to the milbase as disruption energy and asfrictional energy in the form of heat. In order safely to remove thislarge quantity of heat it is necessary to take constructional measuresto keep the ratio of milling space to milling-chamber surface area(cooling area) as low as possible. At high throughputs, milling iscarried out in circulation and the heat is dissipated to the outsidepredominantly via the milbase. Grinding media used include beads ofzirconium oxide, zirconium mixed oxide, aluminum oxide or quartz with adiameter of less than or equal to 0.9 mm; it is advantageous to usethose having a diameter of from 0.2 to 0.9 mm, preferably from 0.3 to0.5 mm.

When continuous stirred ball mills are used for the fine division thegrinding media are separated from the milbase preferably by centrifugaldeposition, so that there is virtually no contact between the separationdevices and the grinding media, thus making it possible to a largeextent to prevent the separation devices becoming blocked. In this casethe stirred ball mills are operated with a high grinding media charge.In the case of the continuous stirred ball mills the milling chamber isfilled almost completely with grinding media.

The milling duration is dependent on the fineness requirements and onthe requirements regarding the performance properties for the particularfield of use. Accordingly the residence time of the milbase in thestirred ball mill is generally between 3 and 60 minutes. It normallyruns to a duration of 4 and 45 minutes, preferably from 5 to 30 minutes.

Milling, vatting and reoxidation are advantageously conducted attemperatures in the range from 0 to 100° C., advantageously at atemperature between 10 and 60° C, preferably at from 20 to 50° C.

The liquid medium in the method of the invention is advantageouslywater. However, it is also possible to use an aqueous-organic medium.Suitable organic solvents include alcohols having 1 to 10 carbon atoms,such as methanol, ethanol, n-propanol, isopropanol, butanols, such asn-butanol, isobutanol and tert-butanol, pentanols, such as n-pentanoland 2-methyl-2-butanol, hexanols, such as 2-methyl-2-pentanol,3-methyl-3-pentanol, 2-methyl-2-hexanol, 3-ethyl-3-pentanol, octanols,such as 2,4,4-trimethyl-2-pentanol, cyclohexanol; or glycols, such asethylene glycol, diethylene glycol, propylene glycol, dipropyleneglycol, or glycerol; polyglycols, such as polyethylene or polypropyleneglycols; ethers, such as methyl isobutyl ether, tetrahydrofuran,dimethoxyethane or dioxane; glycol ethers, such as monomethyl ormonoethyl ethers of ethylene or propylene glycol, diethylene glycolmonomethyl ether, diethylene glycol monoethyl ether, butyl glycols ormethoxybutanol; ketones, such as acetone, diethyl ketone, methylisobutyl ketone, methyl ethyl ketone or cyclohexanone; aliphatic acidamides, such as formamide, dimethylformamide, N-methylacetamide orN,N-dimethylacetamide; urea derivatives, such as tetramethylurea; orcyclic carboxamides, such as N-methylpyrrolidone, valerolactam orcaprolactam; esters, such as carboxylic acid C₁-C₆ alkyl esters, such asbutyl formate, ethyl acetate or propyl propionate; or carboxylic acidC₁-C₆ glycol esters; or glycol ether acetates, such as1-methoxy-2-propyl acetate; or phthalic or benzoic acid C₁-C₆ alkylesters, such as ethyl benzoate; cyclic esters, such as caprolactone;nitriles, such as acetonitrile or benzonitrile; aliphatic or aromatichydrocarbons, such as cyclohexane or benzene; or alkyl-, alkoxy-, nitro-or halogen-substituted benzene, such as toluene, xylenes, ethylbenzene,anisole, nitrobenzene, chlorobenzene, o-dichlorobenzene,1,2,4-trichlorobenzene or bromobenzene; or other substituted aromatics,such as benzoic acid or phenol; aromatic heterocycles, such asmorpholine, picoline or quinoline; and also hexamethylphosphoramide,1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide and sulfolane.

Particular preference is given to water and mixtures of C₁-C₆ alcohols,N-methylpyrrolidone, nitrobenzene and/or toluene with water. Whenselecting the solvents it is important to ensure that they are stableunder the chosen conditions.

Following complete oxidation and the end of milling the pigments areisolated in customary fashion by filtration. Prior to isolation of apigment it is possible for any solvent used to be removed bydistillation, where appropriate under reduced pressure, or else by steamdistillation.

The pigments produced by the method of the invention can be employed aspreferably aqueous presscakes, but in general are solid systems offree-flowing powder kind, or granules.

The coloristic properties can be enhanced, and certain performanceeffects obtained, by using auxiliaries such as, for example,surfactants, pigmentary and nonpigmentary dispersants, fillers,standardizers, resins, waxes, defoamers, antidust agents, extenders,shading colorants, preservatives, drying retardants, rheology controladditives, wetting agents, antioxidants, UV absorbers, lightstabilizers, or a combination thereof.

Auxiliaries can be added at any desired point in time before, during orafter the reduction, oxidation or isolation, all at once or in two ormore portions. The total amount of auxiliaries added can amount to from0% to 40% by weight, preferably from 1 % to 30% by weight, morepreferably from 2.5% to 25% by weight, based on the pigment.

Suitable surfactants include anionic or anion-active, cationic orcation-active and nonionic substances, or mixtures of these agents.Preference is given to those surfactants or surfactant mixtures which donot foam in the course of milling, reduction and oxidation.

Examples of suitable anionic substances include fatty acid taurides,fatty acid N-methyltaurides, fatty acid isethionates,alkylphenylsulfonates, alkylnaphthalenesulfonates, alkylphenolpolyglycol ether sulfates, fatty alcohol polyglycol ether sulfates,fatty acid amide polyglycol ether sulfates, alkylsulfosuccinamates,alkenylsuccinic monoesters, fatty alcohol polyglycol ethersulfosuccinates, alkanesulfonates, fatty acid glutamates,alkylsulfosuccinates, fatty acid sarcosides; fatty acids, examples beingpalmitic, stearic and oleic acid; soaps, examples being alkali metalsalts of fatty acids, naphthenic acids and resin acids, such as abieticacid, alkali-soluble resins, examples being rosin-modified maleateresins and condensation products based on cyanuric chloride, taurine,N,N′-diethylaminopropylamine and p-phenylenediamine. Particularpreference is given to resin soaps, i.e., alkali metal salts of resinacids. Examples of suitable cationic substances include quaternaryammonium salts, fatty amine alkoxylates, alkoxylated polyamines, fattyamine polyglycol ethers, fatty amines, diamines and polyamines derivedfrom fatty amines or fatty alcohols, and the alkoxylates of said amines,imidazolines derived from fatty acids, and salts of these cationicsubstances, such as acetates, for example.

Examples of suitable nonionic substances include amine oxides, fattyalcohol polyglycol ethers, fatty acid polyglycol esters, betaines, suchas fatty acid amide N-propyl betaines, phosphoric esters of aliphaticand aromatic alcohols, fatty alcohols or fatty alcohol polyglycolethers, fatty acid amide ethoxylates, fatty alcohol-alkylene oxideadducts and alkylphenol polyglycol ethers.

By nonpigmentary dispersants are meant substances which in structuralterms are not derived from organic pigments. They are added asdispersants either during the actual preparation of pigments or else inmany cases during the incorporation of the pigments into the applicationmedia to be colored: for example, during the preparation of paints orprinting inks by dispersing of the pigments into the correspondingbinders. They may be polymeric substances, such as polyolefins,polyesters, polyethers, polyamides, polyimines, polyacrylates,polyisocyanates, block copolymers thereof, copolymers of thecorresponding monomers or polymers of one class modified with a fewmonomers with a different class. These polymeric substances carry polaranchor groups such as hydroxyl, amino, imino and ammonium groups,carboxylic acid and carboxylate groups, sulfonic acid and sulfonategroups or phosphonic acid and phosphonate groups, and can also bemodified with aromatic non-pigmentary substances. Nonpigmentarydispersants may additionally be aromatic substances modified chemicallywith functional groups but not derived from organic pigments.Nonpigmentary dispersants of this kind are known to the skilled workerand in some cases are available commercially (e.g., Solsperse®, Avecia;Disperbyk®, Byk, Efka®, Efka). A number of types will be mentioned belowas representatives; however, it is possible in principle to use anydesired other substances described, examples being condensation productsof isocyanates and alcohols, diols or polyols, amino alcohols ordiamines or polyamines, polymers of hydroxycarboxylic acids, copolymersof olefin monomers or vinyl monomers and ethylenically unsaturatedcarboxylic acids and carboxylic esters, urethane-containing polymers ofethylenically unsaturated monomers, urethane-modified polyesters,condensation products based on cyanuric halides, polymers containingnitroxyl compounds, polyesteramides, modified polyamides, modifiedacrylic polymers, dispersants with comblike structure formed frompolyesters and acrylic polymers, phosphoric esters, polymers derivedfrom triazine, modified polyethers, or dispersants derived fromaromatic, non-pigmentary substances. These base structures are in manycases modified further, by means for example of chemical reaction withfurther substances which carry functional groups, or by formation ofsalts.

By pigmentary dispersants are meant pigment dispersants which derivefrom an organic pigment base structure and are prepared by chemicalmodification of said base structure; examples include pigmentdispersants containing saccharin, piperidyl-containing pigmentdispersants, naphthalene- or perylene-derived pigment dispersants,pigment, dispersants containing functional groups linked to the pigmentbase structure via a methylene group, pigment base structures modifiedchemically with polymers, pigment dispersants containing sulfo acidgroups, sulfonamide groups or sulfo acid ester groups, pigmentdispersants containing ether or thioether groups, or pigment dispersantscontaining carboxylic acid, carboxylic ester or carboxamide groups.

It is also possible to follow milling by a finish treatment, whereappropriate using organic solvents, at elevated temperature.

It was surprising that the inventive combination of vatting and millingis accompanied, for a given milling duration, by attainment ofsignificantly greater effects, such as high transparency, for example.As a result it is also possible to reduce the milling duration. For thepreparation of the pigments the use of solvents or auxiliaries is notmandatory in the method of the invention. The amount of salt producedcan be significantly reduced in comparison with the prior art.

The pigments of the invention, when used for coloring high molecularmass organic materials, are distinguished by outstanding performanceproperties, in particular by outstanding rheology, ready dispersibility,high transparency, good gloss behavior, high color strength, excellentbleedfastnesses and overcoating fastnesses, and very good lighffastnessand weatherfastness.

The pigments produced by the method of the invention can be employed forpigmenting high molecular mass organic materials of natural or syntheticorigin, such as plastics, resins, varnishes, paints orelectrophotographic toners and developers, and also drawing, writing andprinting inks.

Examples of high molecular mass organic materials that can be pigmentedwith said pigments are cellulose ethers and cellulose esters, such asethylcellulose, nitrocellulose, cellulose acetate or cellulose butyrate,natural resins or synthetic resins, such as addition-polymerizationresins or condensation resins, examples being amino resins, especiallyurea-formaldehyde and melamine-formaldehyde resins, alkyd resins,acrylic resins, phenolic resins, polycarbonates, polyolefins, such aspolystyrene, polyvinyl chloride, polyethylene, polypropylene,polyacrylonitrile, polyacrylic esters, polyamides, polyurethanes orpolyesters, rubber, caseine, silicone and silicone resins, individuallyor in mixtures.

It is irrelevant whether the aforementioned high molecular mass organiccompounds are in the form of plastic masses, melts or in the form ofspinning solutions, varnishes, paints or printing inks. Depending on theintended use it is found advantageous to utilize the pigments obtainedin accordance with the invention in the form of a blend or in the formof preparations or dispersions. Based on the high molecular mass organicmaterial to be pigmented, the pigments of the invention are used in anamount of from 0.05% to 30% by weight, preferably from 0.1% to 15% byweight.

The pigments produced in accordance with the invention are also suitableas colorants in electrophotographic toners and developers, such asone-component or two-component powder toners (also called one-componentor two-component developers), magnetic toners, liquid toners,polymerization toners and specialty toners, for example.

Typical toner binders are addition-polymerization resins, polyadditionresins and polycondensation resins, such as styrene, styrene-acrylate,styrene-butadiene, acrylate, polyester and phenol-epoxy resins,polysulfones, polyurethanes, individually or in combination, and alsopolyethylene and polypropylene, which may also already include, or bemodified subsequently with, further ingredient additions, such as chargecontrol agents, waxes or flow assistants.

The pigments produced in accordance with the invention are furthersuited to use as colorants in powders and powder coating materials,particularly in triboelectrically or electrokinetically sprayable powdercoating materials which are employed to coat the surfaces of articlesmade, for example, from metal, wood, plastic, glass, ceramic, concrete,textile material, paper or rubber.

Resins used as powder coating resins are typically epoxy resins,carboxyl- and hydroxyl-containing polyester resins, polyurethane resinsand acrylic resins, together with customary curatives. Resincombinations also find use. Thus, for example, epoxy resins arefrequently employed in combination with carboxyl- andhydroxyl-containing polyester resins. Typical curative components(depending on the resin system) are, for example, acid anhydrides,imidazoles and also dicyandiamide and its derivatives, blockedisocyanates, bisacylurethanes, phenolic and melamine resins, triglycidylisocyanurates, oxazolines and dicarboxylic acids. The pigments producedin accordance with the invention are also suitable for use as colorantsin ink-jet inks, on both an aqueous and a nonaqueous basis, and also inthose inks which operate in accordance with the hot-melt process.

Additionally the pigments produced in accordance with the invention arealso suitable for use as colorants for color filters, and also for bothadditive and subtractive color generation.

To assess the properties of the pigments in the plastics field, aselection was made, from among the multiplicity of known plastics, ofplasticized polyvinyl chloride (PVC). The bleedfastness was determinedin accordance with DIN 53775.

To assess the properties of the pigments in the coatings sector, aselection was made, from among the multiplicity of known varnishes, ofan alkyd-melamine resin varnish based on a medium-oil alkyd resin and ona butanol-etherified melamine resin (AM) and also of a high-solidsacrylic resin stoving varnish based on a nonaqueous dispersion (HS).

The color strength and shade were determined in accordance with DIN55986.

The millbase rheology after dispersion was evaluated visually on thebasis of the following five-point scale:

-   -   5 highly fluid    -   4 liquid    -   3 viscous    -   2 slightly set    -   1 set

The fastness to overcoating was determined in accordance with DIN 53221.

The determination of the viscosity was made after dilution of themillbase to the final pigment concentration, using the Rossmannviscospatula type 301 from Erichsen.

In the examples below parts and percentages are by weight in each case.

EXAMPLE 1

10 parts of crude perylenetetracarboxylic bis-p-phenetidide (P.R.123,C.I. No. 71145), prepared according to DE-1 113 773 example 1, aresuspended in 74 parts of water. Following addition of 8 parts of 100%sodium hydroxide, 8 parts of 100% sodium dithionite and 360 parts ofzirconium mixed oxide beads of diameter 0.3-0.4 mm as grinding media,the suspension is charged to a stirred ball mill (manufacturer:Draiswerke GmbH, Mannheim) and milled for 10 minutes at 20° C. with aperipheral speed of 15.7 m/s and a power density of 3.1 kW/l millingspace. Thereafter the grinding media are separated from the millbase bysieving. The suspension is heated to 60° C. It is admixed with 28.6parts of Perhydrol in 35% form, heated to 80° C and stirred at 80° C for2 h. Then it is filtered with suction and the solid product is washedwith water and dried at 80° C.

This gives about 9 parts of pigment, which in plastic (PVC) yieldsstrong, transparent colorations of good dispersibility (no bits) andexcellent bleedfastness.

EXAMPLE 2

The procedure of example 1 is repeated with the sole difference thatinstead of the 28.6 parts of Perhydrol 90 parts of Perhydrol in 35% formare used.

This gives about 9 parts of pigment, which in plastic (PVC) yieldsstrong, transparent colorations of good dispersibility (no bits) andexcellent bleedfastness.

EXAMPLE 3a, COMPARATIVE EXAMPLE (DRY MILLING WITH SALT, NO VATTING)

A plastic container filled to 80% by volume with 1400 parts of steatitecylinders 12 mm in diameter and 12 mm in length as grinding media, ischarged with 30 parts of crude perylenetetracarboxylicbis-p-phenetidide, prepared according to DE-1 113 773 example 1, and 90parts of sodium sulfate. Milling to a fine degree takes place for 8hours with shaking on a vibratory mill (Vibratom type; manufacturer:Siebtechnik Mohlheim) at 1400 revolutions per minute, vibration circle 4mm. The millbase is separated from the grinding media by sieving andintroduced into 2000 parts of water. 33% strength sodium hydroxidesolution is used to set a pH of 11.5, after which the aqueous millbaseis stirred at 80° C. for 2 hours and filtered with suction and the solidproduct is washed free of salt and dried at 80° C. This gives 25.6 partsof pigment. The colorations in plastic (PVC), compared with those ofexample 2, are much more opaque and substantially darker.

EXAMPLE 3b, COMPARATIVE EXAMPLE (INVENTIVE MILLING, NO VATTING)

10 parts of crude perylenetetracarboxylic bis-p-phenetidide (P.R.123,C.I. No. 71145), prepared according to DE-1 113 773 example 1, aresuspended in 96 parts of water. Following addition of 4 parts of 100%sodium hydroxide and 360 parts of zirconium mixed oxide beads ofdiameter 0.3-0.4 mm as grinding media, the suspension is charged to astirred ball mill (manufacturer: Draiswerke GmbH, Mannheim) and milledfor 10 minutes at 20° C. with a peripheral speed of 15.7 m/s and a powerdensity of 3.1 kW/l milling space. Thereafter the grinding media areseparated from the millbase by sieving. The suspension is filtered withsuction and the pigment is washed with water and dried at 80° C. Thisgives about 9.5 parts of pigment, which in plastic (PVC), compared tothe colorations from example 1, yields colorations which aresubstantially more opaque, darker and bluer.

EXAMPLE 4

10 parts of coarsely crystalline crude 4,10-dibromoanthanthrone pigment(P.R.168, C.I.

No. 59300), prepared according to Fiat Final Report 1313 Vol. II, aresuspended in 90 parts of water. Following addition of 8 parts of 100%sodium hydroxide, 9.3 parts of 86% sodium dithionite and 360 parts ofzirconium mixed oxide beads of diameter 0.3-0.4 mm as grinding media,the suspension is charged to a stirred ball mill (manufacturer:Draiswerke GmbH, Mannheim) and milled for 10 minutes at 20° C. with aperipheral speed of 15.7 m/s and a power density of 3.1 kW/l millingspace. Thereafter the grinding media are separated from the millbase bysieving. 90.8 parts of Perhydrol in 35% form are admixed to thesuspension and the mixture is stirred for 1 h. Then it is filtered withsuction and the solid product is washed with water and dried at 80° C.

This gives 6.1 parts of pigment, which in the AM varnish yields stronglycolored, transparent coatings with a yellowish red shade. The glossmeasurement produces a value of 77 and the viscosity is 5.1 s.

EXAMPLE 5, COMPARATIVE EXAMPLE (INVENTIVE MILLING, NO VATTING)

The procedure described in example 4 is repeated with the differencethat no sodium dithionite is added; instead, a pH of 12 is set using 33%strength sodium hydroxide.

This gives 9.3 parts of pigment, which in the AM varnish, as comparedwith the pigment prepared according to example 4, yields coatings whichare significantly more opaque and much bluer; the gloss measurementgives a lower value of 54, and the viscosity is higher and is 6.6 s.

EXAMPLE 6a, COMPARATIVE EXAMPLE (INVENTIVE MILLING, NO VATTING)

10 parts of commercially customary, coarsely crystalline crudeindanthrone pigment (P.B. 60, C.I. No. 69800, prepared for exampleaccording to BIOS 987, 4, 52/4; FIAT 1313, 2, 73) are suspended in 90parts of water. A pH of 12 is set using 33% strength sodium hydroxidesolution. Following addition of 360 parts of zirconium mixed oxide beadsof diameter 0.3-0.4 mm as grinding media the suspension is charged to astirred ball mill (manufacturer: Draiswerke GmbH, Mannheim) and ismilled at 20° C. for 10 minutes with a peripheral speed of 15.7 m/s anda power density of 3.1 kW/l milling space. Thereafter the grinding mediaare separated from the millbase by sieving and the pigment is filteredoff with suction, washed with water and dried at 80° C. This gives 9.2parts of pigment.

EXAMPLE 6b

10 parts of the crude indanthrone pigment likewise used in example 6aare suspended in 74 parts of water. Following the addition of 8 parts of100% sodium hydroxide, 9.3 parts of 86% sodium dithionite and 360 partsof zirconium mixed oxide beads of diameter 0.3-0.4 mm as grinding mediathe suspension is charged to a stirred ball mill (manufacturer:Draiswerke GmbH, Mannheim) and is milled at 20° C. for 10 minutes with aperipheral speed of 15.7 m/s and a power density of 3.1 kW/l millingspace. Thereafter the grinding media are separated from the millbase bysieving. Then at room temperature 90 parts of Perhydrol in 35% form areadded and the mixture is stirred for 1 h. It is then filtered withsuction and the solid product is washed with water and dried at 80° C.

This gives 9 parts of pigment, which in the HS varnish yields stronglycolored, transparent coatings with a reddish shade. The metallic coatingis brilliant and reddish. Compared with the coating made using thepigment prepared according to example 6a, the masstone coating issignificantly more transparent, the white reduction is significantlystronger in color and much more reddish, and the metallic coating islikewise much more reddish.

EXAMPLE 7

10 parts of a coarsely crystalline crude perylene pigment P.R.149, C.I.No. 71137, prepared according to DE-1 067 157, are suspended in 74 partsof 20% strength aqueous tert-amyl alcohol. Following addition of 8 partsof 100% sodium hydroxide, 9.3 parts of 86% sodium dithionite and 360parts of zirconium mixed oxide beads of diameter 0.3-0.4 mm as grindingmedia, the suspension is charged to a stirred ball mill (manufacturer:Draiswerke GmbH, Mannheim) and milled for 30 minutes at 20° C. with aperipheral speed of 15.7 m/s and a power density of 3.1 kW/l millingspace. Thereafter the grinding media are separated from the millbase bysieving. The suspension is heated to 60° C., admixed with 90 parts ofPerhydrol in 35% form, heated to 80° C. and stirred at 80° C. for 2 h.The amyl alcohol is removed by steam distillation and the pigment isfiltered off with suction, washed with water and dried at 80° C.

This gives about 9 parts of pigment, which in plastic (pvc) yieldsstrong, transparent colorations of good dispersibility (no bits) andexcellent bleedfastness.

1) A method of producing a vattable organic pigment comprising the stepsof vatting an aqueous or aqueous-organic suspension of a coarselycrystalline crude pigment and reoxidizing it the aqueous oraqueous-organic suspension of a coarsely crystalline crude pigment,wherein at least one of the steps of vatting and reoxidizing furthercomprises milling the aqueous or aqueous-organic suspension of acoarsely crystalline crude pigment, with a stirred ball mill operatedwith a power density of more than 1.0 kw per liter of milling space andwith a peripheral stirrer speed of more than 12 m/s, under the action ofgrinding media with a diameter of less than or equal to 0.9 mm. 2) Themethod as claimed in claim 1, wherein the coarsely crystalline pigmentis selected from the group consisting of indanthrone, anthanthrone,thioindigo, perinone and perylene pigments. 3) The method as claimed inclaim 1, wherein the coarsely crystalline pigment is C.I. Pigment Blue60, 66, C.I. Pigment Red 88, 168, 123, 149, 178, 179, 181, 189, 194,C.I. Vat Red 14, 41, C.I. Pigment Orange 43, C.I. Pigment Violet 29,C.I. Pigment Black 31 or 32, mixture thereof or a mixed crystal thereof.4) The method as claimed in claim 1, wherein the vatting step occurswith sodium dithionite or potassium dithionite. 5) The method as claimedin claim 1, wherein the pigment concentration in the suspension is from2.5% to 40% by weight, based on the total weight of the suspension. 6)The method as claimed in claim 1, wherein the milling duration isbetween 3 and 60 minutes. 7) The method as claimed in claim 1, whereinvatting, oxidation and milling are conducted at a temperature between 0and 100° C. 8) The method as claimed in claim 1, wherein the suspensioncomprises water or a mixture of C₁-C₆ alcohols, N-methylpyrrolidone,toluene and/or nitrobenzene with water. 9) The method as claimed in atclaim 1, wherein at least one of the vatting and reoxidizing stepsfurther comprises adding at least one auxiliary selected from the groupconsisting of surfactants, pigmentary and nonpigmentary dispersants,fillers, standardizers, resins, waxes, defoamers, antidust agents,extenders, shading colorants, preservatives, drying retardants, rheologycontrol additives, wetting agents, antioxidants, UV absorbers, lightstabilizers and a combination thereof. 10) The method as claimed inclaim 1, wherein milling occurs during at least the vatting step andwherein the leuco compound formed during the vatting step is milled inthe form of its salt or in the form of its acid. 11) A vattable organicpigment made in accordance with the method of claim
 1. 12) A highmolecular mass organic material comprising a vattable organic pigment asclaimed in claim
 11. 13) The high molecular mass organic material asclaimed in claim 12, wherein the high molecular mass organic material isselected from the group consisting of plastics, resins, varnishes,paints, electrophotographic toners, electrophotographic developers,drawing inks, printing inks and writing inks.